FIG. 1 shows a hydraulic control system used in a lift truck. A pump 16 pumps hydraulic fluid from a tank 14 into a Priority Flow Divider (PFD) 18. The PFD 18 maintains a hydraulic Priority Flow (PF) to a Steering Control Unit (SCU) 38. An Excess Flow (EF) is sent to a hydraulic control valve 28.
The SCU 38 uses the hydraulic fluid from PFD 18 to control a hydraulic piston 48 that controls the direction of wheels 50. For example, when a steering wheel 44 is turned in a first direction, the SCU 38 may direct hydraulic fluid into a first hydraulic hose 40 connected to a first side 54 of the hydraulic piston 48. The hydraulic fluid in hose 40 causes the piston 48 to turn the wheels 50 in a first direction. Hydraulic fluid located in the opposite side 52 of piston 48 exits through hose 42 back to the SCU 38 and then out hose 46 to tank 14.
If steering wheel 44 is turned in the opposite direction, the SCU 38 directs hydraulic fluid through hose 42 into side 52 of piston 48. The fluid in hose 42 causes the piston 48 to turn the wheels 50 in the opposite direction. The hydraulic fluid in side 54 of piston 48 exits through hose 40 through the SCU 38 and hose 46 back to tank 14.
The EF flow from PFD 18 goes through hose 26 to the control valve 28. The control valve 28 uses the hydraulic fluid to control a hydraulic actuator 31. The returning hydraulic fluid from the hydraulic actuator 31 returns back to the control valve 28 and then travels out hose 36 to the hydraulic fluid tank 14.
The control valve 28 and hydraulic actuator 31 can be used to control any type of hydraulic equipment, but is shown in one example in FIG. 1 controlling a fork lift mast 32. The items 20, 22, 24, 26, 33, 36, 40, 42, and 46 are described as hydraulic fluid hoses but can be any type of fluid conductor, such as tubes, pipes, etc., that direct hydraulic fluid between the different components in the hydraulic control system 12.
The hydraulic system shown in FIG. 1 requires a large number of hydraulic hoses. For example, hoses 20 and 22 are needed to supply hydraulic fluid to PFD 18. Hoses 24 and 26 are required to transport hydraulic fluid to the SCU 38 and the control valve 28, respectively. In addition to using the hose 24, the SCU 38 also requires the two steering piston hoses 40 and 42 and a return tank hose 46. For a load sensing PFD, another load sense hose 25 is required between the PFD 18 and the SCU 38. In addition to the hydraulic actuator hoses 33, the control valve 28 uses hose 26 from the PFD 18 and a tank return hose 36.
These hydraulic hoses, tubes, pipes, etc. add expense to the hydraulic system. For example, added time is required to fabricate and install all of the hoses to the different hydraulic components. Each end of each hydraulic hose requires connector fittings that have the potential of oil leakage. The long lengths of the hoses between the different hydraulic components can also reduce hydraulic pressure in the system, in turn, reducing the response time of the hydraulic equipment. To improve response time, hydraulic pressure must then be increased in the hydraulic system.
The present invention addresses this and other problems associated with the prior art.